Gas turbine engines are well known internal combustion engines typically used to provide thrust to an aircraft or to provide power for land-based operations. Generally speaking, a gas turbine engine includes a fan, a compressor, a combustor and a turbine arranged in a serial fashion. The fan draws in ambient air as it rotates and moves it to the compressor where the air is compressed or pressurized. The compressed air is then communicated to the combustor where it is mixed with fuel and ignited. The products of the combustion are hot gases which are then directed into the turbine. This causes the airfoils in the turbine to rotate, and as turbine is mounted on the same shaft, or shafts, as the compressor and fan, this causes the compressor and fan to rotate as well. Accordingly, once started, it can be seen that the operation of the engine is self-sustaining in that the combustion of more fuel causes more rotation of the turbine and in turn the compressor and the fan. Moreover, the rotation of the fan, which typically has a diameter many times that of the compressor and the turbine, causes the engine to generate thrust.
During operation, ice can form and build-up on fan blades and their roots, such as when an aircraft is in a holding pattern and the blades are rotating at a relatively low speed. Then, when the aircraft is given clearance to leave the pattern, the subsequent acceleration of the engine may cause the ice to peel away from the blades and roots and hurl into the fan casing, thereby causing denting, or other damage, that leads to decreased operational efficiency in the engine. To alleviate such operational efficiency issues, engine manufacturers ordinarily place impact liners inside the fan casing that absorb the energy of impacting material. These impact liners can then be replaced so that the efficiency of the engine can be maintained.
In addition to issues with ice, gas turbine engine designers also face increasing pressure to further attenuate noise, such as fan tones and fan broadband, heard on approach/takeoff from airports and by passengers inside the cabin during flight. To lessen such noise, engine designers customarily place acoustic panels aft the impact liners discussed above. While effective and widely used, a problem with the afore-mentioned impact liners is that they ordinarily do not attenuate noise, and therefore take up space that could be used for placement of additional acoustic panels to help lessen such engine noise.
Thus, while certain gas turbine engine impact panels are known, improvements to impact liners in the area of noise attenuation, while maintaining resilience to ice damage, is desired.